Natural gas from foreign countries is shipped to this country in liquid form to save space. In its gaseous state its volume is on the order of 500 times its liquid volume. To retain the gas in its liquid form it must be retained at cryogenic temperatures. Some temperatures, however, cause imbrittlement of the storage tank steel. Hence the need for improved insulation in the tanks.
Foam insulation layers were first applied to the tank interior walls. However, as the liquid gas would penetrate the foam, heat up and expand, the gas would rip off chunks of insulation. The problem was solved by using a matrix of three-dimensional fibers within the foam and bonded securely to the tank wall. Several methods have been devised in accomplishing this.
One method of manufacturing a three-dimensional fabric reinforced foam insulation is to position several layers of open weave fabric netting in spaced stacked relationship and lock the layers together with tufting stitching. This passes multiple loops of threads through the layers. Thereafter the foaming operation embeds the matrix in the foam insulation which then may be used after it has cured.
In making blocks of insulation, the multiple layers of fabric are suspended in stacked frames of desired size. After foaming and curing, the frames are cut from the blocks and cleaned for re-use or are discarded. This is a low-volume production technique.
A high-volume endless strip of insulation on a low cost production basis is needed to place the aforementioned three-dimensional insulation in a financially competitive position. A method and apparatus must be developed for this purpose.